The present invention relates to cordless blinds. More particularly, the present invention relates to a variable friction device for a cordless blind.
It is generally known to provide for a window covering venetian blind with the slats that are raised and lowered by a pair of lift cords. Such known window coverings typically include lift cords that are secured to a bottom rail and extend upward through the slats into a head rail. The lift cords are guided within the head rail and exit through a cord lock and hang outside of the window covering. In order to raise or lower the window covering, the lift cords are manipulated to first release the cord lock. Similarly, once the window covering has been raised or lowered the cord lock is manipulated again to lock the cords in place. However, such an arrangement may present a safety concern to small children and pets.
Blinds and shades in which the lift cords are contained within the bottom rail, window covering and head rail are referred to as xe2x80x9ccordlessxe2x80x9d blinds and shades because no portion of the lift cords is external to the blind or shade. Cordless blinds have been gaining popularity and are employed in a wide variety of blinds and shades such as venetian blinds, cellular blinds, pleated shades, and wood blinds. One type of cordless blind disclosed in U.S. Pat. Nos. 5,482,100; 5,531,257; and 6,079,471, and incorporated herein, utilizes a spring motor to apply a spring force to the lift cords to bias the bottom rail and accumulated window covering toward the top rail.
In a xe2x80x9cbalancedxe2x80x9d cordless blind system, the spring force of the spring motor is balanced by the combined weight of the bottom rail (and any accumulated window covering) and friction, sometimes misidentified in the field as inertia. If the system is not in balance, the bottom bar will either move upward or downward depending on the imbalance in the system. For example if the spring force is greater than the weight of the bottom bar (and accumulated window covering) and the frictional forces in the system, then the bottom bar will continue to be biased upward toward the head rail, until the weight of the accumulated window covering balances the system. Similarly, if the spring force and frictional system forces are less than the weight of the bottom bar and accumulated window covering the bottom bar will move downward away from the head rail.
In such balanced cordless blind systems the frictional force is greater than the difference between the spring force and the combined weight of the bottom rail and accumulated window covering when the bottom rail is at any location between a fully raised position (open) and a fully lowered position (closed).
Because the weight of the accumulated window covering increases as the bottom bar moves toward the head rail, the minimum weight occurs when the bottom rail is fully lowered (closed). The friction that is inherent or that is added (e.g., designed into or introduced) to the system needs to be at least sufficient to offset this minimum weight condition, and prevent undesired movement toward the head rail. To prevent the bottom rail from undesirable upward movement, the total friction of the system must be sufficient to resist forces generated by oversized spring motors (which are included to accommodate a variety of sizes of window coverings). Accordingly, because most of the operation of the blind is where the blind is between the fully raised and fully lowered positions, the system has more friction than is necessary to balance it. However, operator force necessary to overcome excess friction may damage the window covering, the head rail, the spring motor, or the mounting brackets, and the like. Also, while a blind with a superfluous amount of friction will operate (so long as there is sufficient spring force to retract the liftcords), it is unduly and unnecessarily laborious for the user.
Accordingly, it would be desirable to provide a cordless blind having a device that would vary the amount of friction introduced into a blind actuation system. It would also be advantageous to provide a cordless blind having a variable friction device, in which the blind could be raised by manual biasing of the bottom rail toward the top rail without releasing a brake. To provide an inexpensive, reliable, and widely adaptable variable friction device for a cordless blind that avoids the above-referenced and other problems would represent a significant advance in the art.
A primary feature of the present invention is to provide an inexpensive, easy-to-manufacture and aesthetically-pleasing balanced cordless blind that overcomes the above-noted disadvantages.
Another feature of the present invention is to provide a device that provides a varying amount of friction to a cordless blind system.
Another feature of the present invention is to provide a variable friction device design that is adaptable to work with a variety of window covering configurations.
Another feature of the present invention is to provide a variable friction device that can be located in the head rail or the bottom rail.
How these and other advantages and features of the present invention accomplished (individually, collectively, or in various subcombinations) will be described in the following detailed description of the preferred and other exemplary embodiments, taken in conjunction with the FIGURES. Generally, however, they are accomplished in a blind including a head rail, a bottom rail, and a window covering located between the head rail and the bottom rail, and a spool and spring motor assembly. The bottom rail is connected to the head rail by two lift cords and is configured to move in a first direction and in a second direction. The spool and spring motor assembly is configured to bias the bottom rail toward the head rail. The blind also includes a variable friction device that includes a pair of first frictional bearing surfaces configured to provide resistance to movement of the two lift cords, a pair of second frictional bearing surfaces configured to provide resistance to movement of the two lift cords, and a biasing member coupled to one of the first frictional bearing surfaces and the second frictional bearing surfaces. The biasing member is configured to expand and contract based on the direction of movement of the bottom rail. The variable friction device is configured to provide a first friction path for the two lift cords when the bottom rail is moved in the first direction and a second friction path for the two lift cords when the bottom rail is moved in the second direction, the first friction path being different than the second friction path.
These and other advantages and features of the present invention may also be accomplished in a blind including a head rail, a bottom rail, and a window covering located between the head rail and the bottom rail. The bottom rail being connected to the head rail by two lift cords and configured to move in a first direction and a second direction. The blind also includes a variable friction device having a bearing surface configured to provide a first friction force that opposes movement of the two lift cords when the bottom rail is moved in the first direction, and a second friction force that opposes movement of the two lift cords wherein the bottom rail is moved in the second direction. The first friction force is different than the second friction force.
These and other advantages and features of the present invention may also be accomplished in blind including a head rail, a bottom rail, and a window covering located between the head rail and the bottom rail, the bottom rail being connected to the head rail by a pair of lift cords and configured to move in a first direction and a second direction. The blind also includes a first bearing surface and a second bearing surface defined by the contact surface area between the two lift cords and the first and second bearing surfaces, and means for varying the friction force between the first and second bearing surfaces and the left cords.
The present invention further relates to various features and combinations of features shown and described in the disclosed embodiments. Other ways in which the objects and features of the disclosed embodiments are accomplished will be described in the following specification or will become apparent to those skilled in the art after they have read this specification. Such other ways are deemed to fall within the scope of the disclosed embodiments if they fall within the scope of the claims which follow.